1. Field of the Invention
The present invention relates to film forming compositions which can be utilized to make vapor barrier films suitable for use in building construction.
2. Description of the Prior Art
Vapor barrier films are specialized products which are commonly used in building construction to retard the transmission of water vapor into or from the interior of the building. They should have a balance of the following characteristics: a low water vapor transmission value; good flame retardancy and low smoke generation properties; good low temperature flexibility; good tensile and tear strength; and easy processability for such forming operations as calendering, extrusion casting, extrusion blow molding, and solvent casting.
One approach to making such films has been the use of an externally plasticized vinyl chloride polymer resin as the polymer component of such films in conjunction with appropriate amounts of flame retardants, fillers, lubricants, stabilizers, and the like (e.g., see Film No. 1 in Table 1 of U.S. Pat. No. 3,983,290 to R. G. Elcik). Although such films show resistance to water vapor transmission, the presence of externally added plasticizer gives rise to the possibility of plasticizer migration and resulting embrittlement of the product with the passage of time.
Another approach to forming such films has been to incorporate chlorinated polyethylene in the polymer component, along with the vinyl chloride polymer, in an effort to reduce the amount of plasticizer needed in the composition. The presence of plasticizer is believed to contribute to water vapor transmission in vapor barrier films (see, Kogyo Kagaku Zasshi, Vol. 64, 349-355 (1961), abstracted in Chem. Abstr., Vol. 57, 4875 f). Some recent examples of vapor barrier film constructions of this type are shown in: U.S. Pat. No. 3,983,290 to R. G. Elcik; copending U.S. Ser. No. 694,271, filed June 9, 1976, to R. G. Elcik and its corresponding issued Belgian Pat. No. 855,443; and U.S. Pat. No. 3,972,041 to M. A. Koerber.